Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$76.75	5.396%	$80.8914	$80.89	$80.90	$80.90
Purchase #2	$166.88	12.853%	$188.3291	$188.33	$188.35	$188.30
Purchase #3	$92.31	4.172%	$96.1612	$96.16	$96.15	$96.20
Purchase #4	$11.93	4.797%	$12.5023	$12.50	$12.50	$12.50
Purchase #5	$71.60	12.747%	$80.7269	$80.73	$80.75	$80.70
Purchase #6	$173.69	10.354%	$191.6739	$191.67	$191.65	$191.70
Purchase #7	$71.28	7.850%	$76.8755	$76.88	$76.90	$76.90
7 purchase totals =	$664.44		$727.1603	$727.16	$727.20	$727.20